1. Field of the Invention
Most of the known processes for removing hydrogen halides from gas mixtures are based on the use of solutions or suspensions of chemicals which bind the hydrogen halides by the absorption principle. In this case, principally solutions and suspensions of alkali metal compounds or alkaline earth metal compounds such as oxides, hydroxides or carbonates are used.
In many absorption processes used industrially, contact of generally hot gases with a liquid absorbent leads to a marked decrease in the gas temperature. Because of the highly corrosive character of many water-containing gas mixtures if the dew point is undershot and the difficult removal of cold gases via a stack, the gas mixture must often be reheated after the absorption, which markedly impairs the energy balance of the process.
In addition, many alkali metal compounds and alkaline earth metal compounds, in particular sodium hydroxide and potassium hydroxide, are extremely aggressive substances, so that safety precautions must be taken in the operation and maintenance of the apparatus for treating the gas mixtures.
Adsorption processes do not have these disadvantages since the temperature is not decreased and thus the dew point is not undershot, for which reason reheating the gas mixture after removal of the hydrogen halides is not necessary. Furthermore, aqueous systems which contain aggressive substances are bypassed in adsorption processes.
2. Description of the Related Art
U.S. Pat. No. 3,278,266 describes the adsorption of hydrogen halide from vapour mixtures of organic compounds. The adsorbent comprises an oxidic compound of the second main group of the Periodic Table of the Elements which is applied to a support and may be regenerated by desorption.
Surprisingly, it has now been found that such an adsorbent offers the possibility of selectively adsorbing hydrogen halide from a sulfur-dioxide-containing gas and thus of separating hydrogen halide from sulfur dioxide.